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CALDAS, L. R.; LIRA, J. S. de M. M.; MELO, P. C. de.; SPOSTO, R. M. Life cycle carbon emissions inventory of brick masonry and light steel framing houses in Brasilia: proposal of design guidelines for low-carbon social housing. Ambiente Construído, Porto Alegre, v. 17, n. 3, p. 71-85, jul./set. 2017. ISSN 1678-8621 Associação Nacional de Tecnologia do Ambiente Construído.

http://dx.doi.org/10.1590/s1678-86212017000300163

71

Life cycle carbon emissions inventory of brick masonry and light steel framing houses in Brasilia: proposal of design guidelines for low-carbon social housing

Inventário de emissões de carbono no ciclo de vida de habitações de alvenaria e light steel framing em Brasília: proposição de diretrizes de projeto para habitações de interesse social de baixo carbono

Lucas Rosse Caldas Júlia Santiago de Matos Monteiro Lira Pedro Corrêa de Melo Rosa Maria Sposto

Abstract his study evaluated the CO2eq emissions during the life cycle of two

social housing projects in the city of Brasilia. A house of ceramic brick

masonry was compared to a light steel framing one. The life cycle

carbon emissions assessment (LCCO2A) with a cradle-to-grave

approach was used. The relation between the thermal performance of the wall

systems and CO2eq emissions in the operational phase of the houses were evaluated

using the DesignBuilder software. In addition, six scenarios composed of three

CO2eq emission factors from the Brazilian electrical grid and two schedules of

occupation of houses (full and part time) were evaluated. The brick masonry house

presented less CO2eq emissions than the light steel framing one. For both houses,

the operational phase was the most significant regarding the total CO2eq emissions

(50% to 70%), followed by the construction (20% to 30%), maintenance (11% to

20%) and end-of-life (lower than 1%) phases. The results also showed the

importance of considering different CO2eq emission factors for the Brazilian

context in the operational phase. Finally, based on the results obtained, design

guidelines for low carbon social housing were proposed.

Keywords: LCCO2A. Social housing. Thermal performance. Design guidelines.

Resumo

Este estudo avaliou as emissões de CO2eq no ciclo de vida de duas habitações de interesse social, uma de alvenaria de blocos cerâmicos e outra de light steel framing. Como metodologia foi utilizada a Avaliação do Ciclo de Vida de Emissões de Carbono (ACVCO2), com o escopo do berço ao túmulo. Foi avaliada a relação entre o desempenho térmico dos sistemas de vedação vertical e emissões de CO2eq na etapa operacional das habitações utilizando o software DesignBuilder. Foram avaliados seis cenários da etapa operacional, compostos de três fatores de emissões de CO2eq da matriz elétrica brasileira e duas agendas de ocupação das habitações. A habitação de alvenaria cerâmica apresentou menores emissões de CO2eq, e para ambas as habitações a etapa operacional se mostrou a mais significativa (50% a 70%), seguida da construção (20% a 30%), manutenção (11% a 20%) e fim de vida (menor que 1%). Os resultados mostraram a importância de se considerarem diferentes fatores de emissões de CO2eq na etapa operacional. Ao final, com base nos resultados obtidos, foram propostas diretrizes de projeto para habitações de interesse social de baixo carbono.

Palavras-chave: ACVCO2. Habitações de interesse social. Desempenho térmico. Diretrizes de projeto.

T

Lucas Rosse Caldas Federal University of Rio de Janeiro

Rio de Janeiro – RJ – Brazil

Júlia Santiago de Matos Monteiro Lira

University of Brasília Brasília –DF – Brazil

Pedro Corrêa de Melo University of Brasília

Brasília –DF – Brazil

Rosa Maria Sposto University of Brasília

Brasília –DF – Brazil

Recebido em 17/11/16

Aceito em 20/03/17

Ambiente Construído, Porto Alegre, v. 17, n. 3, p. 71-85, jul./set. 2017.

Caldas, L. R.; Lira, J. S. de M. M.; Melo, P. C. de.; Sposto, R. M. 72

Introduction

In 2010, buildings accounted for 32% of the total

global final energy use and 19% of energy-related

greenhouse gas (GHG) emissions (LUCON et al.,

2014). The Brazilian residential buildings were

responsible for 21% of the country’s electricity

consumption in 2015 (MINISTÉRIO…, 2016).

Brazil is a developing economy, a factor that

influences the building sector. There is a housing

deficit in the country and to overcome this problem,

the Brazilian government has developed housing

programs in recent decades such as “My house, My

Life” (Minha Casa, Minha Vida) (PAULSEN;

SPOSTO, 2013). Despite failures and criticism

mainly related to the quality of the houses built, this

program was responsible for the construction of

thousands of new homes for people in need, thus

alleviating the housing deficit in the country.

These social housing programs mainly used the

brick masonry system. However, new building

systems, which may be more rational and

productive, are being considered, such as precast

and prefabricated concrete, concrete walls and light

steel framing. The latter has been imported from the

USA and its use is becoming widespread in the

country, due to higher productivity and the dry

construction process (LIMA, 2016).

Nevertheless, it is necessary to define some

environmental criteria, such as embodied energy

and CO2 emissions, water consumption, waste and

others, to help architects and engineers to specify

more environmental sustainable systems

(CARVALHO; SPOSTO, 2012).

According to Cabeza et al. (2014) and Chau, Leung

and Ng (2015), the life cycle assessment (LCA), the

life cycle energy assessment (LCEA) and the life

cycle carbon emissions assessment (LCCO2A) are

some of the available and internationally

widespread methodologies for environmental

assessment in the building sector.

The life cycle assessment (LCA) evaluates all the

resource inputs, including energy, water and

material consumption, and environmental loads,

including CO2 emissions, as well as liquid and solid

wastes of a product or a process

(INTERNATIONAL…, 2006). However, it has

been observed that most of the research about LCA

applied to buildings has focused on energy

consumption and CO2 emissions. Within this

context, more specific tools such as life cycle

energy assessment (LCEA) and life cycle carbon

emissions assessment (LCCO2A) were developed.

LCEA and LCCO2A are simplified versions of

LCA. While the first one focuses only on the

evaluation of energy inputs, the second focuses on

CO2 emissions in different phases of a building’s

life cycle (CHAU; LEUNG; NG, 2015).

In Brazil, most studies of LCCO2A focus on

building materials. Campos, Punhagui and John

(2011) estimated the CO2 emissions from the

transportation of Amazon wood and evaluated the

reduction of net carbon stock, due to this phase in

the production process. Passuelo et al. (2014)

evaluated the carbon footprint of an alternative

laboratory-produced clinker. Saade et al. (2014)

proposed a set of lifecycle-based indicators to

describe eco-efficient building materials, presenting

an important environmental database for Brazilian

building materials, including CO2eq emissions.

Borges et al. (2014) compared Portland cement and

geopolymer concretes obtained from the alkaline

activation of aluminosilicates. Santoro and Kripka

(2016) evaluated CO2 emissions of concrete

production, considering the material (binder, coarse

aggregates, fine aggregates and steel) extraction and

production stages used in the state of Rio Grande do

Sul.

Paulsen and Sposto (2013) evaluated the energy

consumption (embodied and operational energy)

using the LCEA, during the life cycle of a typical

social house in Brazil. Souza et al. (2016) used the

LCA to compare three kinds of wall systems, made

of concrete bricks, ceramic bricks and cast-in-place

concrete. Atmaca and Atmaca (2015) applied the

LCEA and LCCO2A to compare two residential

buildings in Turkey, one located in a rural area and

the other, in the city. Cabeza et al. (2014) and Chau,

Leung and Ng (2015) revised the state of the art

related to the LCA, LCEA and LCCO2A applied to

the building sector.

Caldas (2016) and Caldas and Sposto (2016)

compared one brick masonry and one light steel

framing house in terms of thermal performance and

embodied energy in Brasilia using the LCEA. The

brick masonry house presented a better thermal

performance and lower energy consumption during

its life cycle. The present paper intends to continue

these studies, though focusing on carbon emissions

and analyzing different scenarios for the operational

phase.

Although there are some studies in Brazil

quantifying the energy consumption in a building’s

life cycle, there are fewer studies related to carbon

emissions assessment, considering thermal

performance and taking a cradle-to-grave approach.

Thus, through the LCCO2A methodology, the aim

of this study is to evaluate the CO2eq emissions

during the life cycle of two social housing projects


Life cycle carbon emissions inventory of brick masonry and light steel framing houses in Brasilia 73

located in Brasília. Two different wall systems were

compared: Brazilian conventional ceramic brick

masonry and light steel framing, considering the

buildings’ entire life cycle, called cradle-to-grave in

literature (construction, use and end-of-life phases).

Two important and innovative aims of this study

were:

(a) the consideration of different operational

phase scenarios, in terms of schedules of

occupation of the buildings and different CO2eq

emission factors from the Brazilian electricity

matrix; and

(b) the proposal of some design guidelines for low

carbon social housing based on the quantitative

results of the LCCO2A of buildings.

Methodology

Functional unit, scope and description of the building

The Functional unit (FU) for this study is a house

located in Brasília – DF, with 4 residents (2 adults

and 2 children), an internal floor area of 46 m² and

a 50-year lifespan (minimum value stipulated in the

NBR 15575-1 (ABNT, 2013)). Brasília is situated

in the Brazilian Bioclimatic Zone number 4 (NBR

15220-3 (ABNT, 2005)).

The house project consists of one living room, two

bedrooms, one kitchen, one bathroom and one

outdoor laundry area. There are three internal doors,

two external doors and five windows. The solar

orientation (facing the North) was chosen according

to the worst situation related to thermal gains in the

house, which was obtained in pre-simulations in the

DesignBuilder. The west orientation for the

bedrooms was chosen as presented in Figure 1. The

foundation is not included in this study once it

depends on the characteristics of the soil. Paulsen

and Sposto (2013) adopted the same criteria.

The Brazilian conventional wall system is ceramic

brick masonry with mortar plaster and reinforced

concrete columns and beams, U-value: 2.5 W/m².K.

The light steel framing wall consists of galvanized

steel frames with two oriented strand boards (OSB),

one gypsum fiberboard in the internal area, one

fiber cement board in the external area and an

insulation layer of rock wool, U-value: 0.7 W/m².K,

as presented in Figure 2.

Table 1 below shows the cradle-to-grave scope,

which includes construction (extraction, processing

of raw materials and transportation of the building

materials from factories to the site location),

operation of the building, maintenance and end-of-

life. The results are presented in terms of carbon

dioxide equivalent (CO2eq)1.

Construction phase analysis

The CO2eq emissions in the construction phase were

taken from the literature. For the light steel framing,

Environmental Product Declarations (EPDs) were

used. The waste of building materials during the

construction process was considered. The

construction working process, mainly performed

manually, was not factored in in this study.

Figure 1 - DesignBuilder model of the case study

1For the CO2eq the following global warming potentials (GWP) were considered, according to IPCC (INTERGOVERNMENTAL…, 2013): 1 for CO2, 28 for CH4 and 265 for N2O.



Figure 2 - Comparison between the two wall systems

Table 1 - Phases in the life cycle of the house

Phases Stages Symbols Description

Construction

(ECO2C)

Extraction, processing of raw

materials ECO2E

CO2eq emissions of building materials

production

Transport ECO2T CO2eq emissions of transport from

factories to site location

Use (ECO2U)

Operational ECO2O CO2eq emissions of electrical

equipment and for cooking

Maintenance ECO2M CO2eq emissions of materials used in

maintenance

End-of-life

(ECO2EL)

Demolition/Deconstruction ECO2D CO2eq emissions of demolition or

deconstruction of house

Waste Transport ECO2Tw CO2eq emissions of transport of waste

from site location to landfill

Waste disposal in landfill ECO2L CO2eq emissions of activities for waste

disposal in landfill

Whole life

cycle All stages ECO2TOT

Sum of CO2eq emissions of all stages

of the house life cycle

In Brazil, building materials are commonly

transported by truck. In this case, the value of fuel

consumption of 0.017 L diesel/t.km was adopted, as

presented by Campos, Punhagui and John (2011).

The full truckloads on the outbound route (from the

factory location to the construction site) and half of

the truckloads on the inbound route were recorded,

therefore multiplied by a factor of 1.5. According to

IPCC (INTERGOVERNMENTAL…, 2006) and

MMA (MINISTÉRIO…, 2013), one liter of diesel

is equivalent to 2.63 kg CO2eq, resulting, in the end,

in a transport coefficient of 0.067 kgCO2/t.km. The

Google Maps app was used to calculate the

transport distances, considering the shortest

distance between the construction site and the

building material producers (Table 2).

Use phase analysis

Operational stage

The operational energy and CO2eq emissions were

divided into three parts: electricity used for

equipment, liquefied petroleum gas (LPG) used for

cooking and energy used for air conditioning

(calculated in relation to the thermal performance of

the buildings).

For the cooling simulation, the U-values used for

brick masonry and light steel framing walls were

2.5 W/m².K and 0.7 W/m².K, respectively. For

windows, the U-value 5.6 W/m².K was used (6 mm

glass). Air conditioning appliances (split) were

adopted for rooms in which people normally spend

more time, such as the living room and the

bedrooms. The cooling set point was fixed at 24.3



°C for these areas, according to the comfort zone of

the city of Brasilia, defined by the neutral

temperature equation presented by Pereira and

Assis (2010). The machine efficiency (CoP)

adopted was 2.8, a common value for this kind of

houses in Brazil. Part and full time schedules of

occupation for the living room and bedrooms were

adopted to evaluate the minimum and the maximum

potential energy consumption due to the air

conditioning appliances. The part-time schedule

adopted was from 5 p.m. to 12 a.m. for the living

room, and 12 a.m. to 7 p.m. for the bedrooms.

EnergyPlus through DesignBuilder was used to

evaluate the impact of variations of the external and

internal walls on annual energy use and CO2eq

emissions of the building by dynamic thermal and

energy simulation. After the simulation, the energy

consumption for other electrical equipment (electric

shower, refrigerator, TV, lighting, etc.) was

2414.17 kWh/year.

The results found for air conditioning energy

consumption were:

(a) brick masonry house with part- time schedules

of occupation: 768.21 kWh/year;

(b) brick masonry house with full-time schedules

of occupation: 2228.78 kWh/year;

(c) light steel framing house with part-time

schedules of occupation: 1271.05 kWh/year; and

(d) light steel framing house with full-time

schedules of occupation: 3219.14 kWh/year.

Table 2 - Data on building materials in the studied houses (46 m²)

Building materials Amount

(kg/m²)

Embodied

emissions

intensity

(kgCO2e/kg)

Source Waste (%)

Transport

Distances

(km)

Brick Masonry

Ceramic brick 165.3 0.24 Saade et al. (2014) 15% 97

Mortar plaster 375.5 0.18¹ Saade et al. (2014) 20% 29.7

Concrete 138.3 0.16² Saade et al. (2014) 9% 16.8

Wood (formwork) 28.3 0.96³ Saade et al. (2014) 10% 75

Steel rebar 10.9 1.95 Saade et al. (2014) 10% 843

Light steel framing

Steel structure 1 1.78 Saade et al. (2014) 10% 975

OSB board 71.2 0.963 Saade et al. (2014) 15% 1298

Gypsum fiberboards 49.1 0.22 Knauf¹ (2013b) 9% 1195

Cement fiberboards 44.4 0.36 Knauf¹ (2013a) 9% 213

Rock wool 6.4 0.88 Deutsche Rockwool¹

(2012) 5% 1014

Other systems of the house

Paint (internal and external

walls) 4.9 1.99 Saade et al. (2014) 15% 224

PVC (installations) 3.6 9.85 Saade et al. (2014) 5% 165

Ceramic tile (roof) 67.1 0.13 Saade et al. (2014) 10% 337

Wood (roof) 17.2 0.114 Saade et al. (2014) 4% 687

PVC (ceiling) 2.4 9.85 Saade et al. (2014) 5% 225

Cement CPII (floor) 14.2 0.66 Votorantim Cimentos

(2016) 20% 30

Sand (floor) 69.2 0.01 Santoro e Kripka (2016) 20% 277

Adhesive mortar 4.9 0.99 Saade et al. (2014) 5% 30

Ceramic tile (floor) 10.9 0.24 Saade et al. (2014) 6% 740

Steel (windows and

external doors) 14.4 1.95

Saade et al. (2014) 2% 214

Glass (windows) 1.6 1.00 Saade et al. (2014) 1% 214

Wood (internal doors) 8.6 0.96³ Saade et al. (2014) 1% 222

Note: Legenda: ¹Only cradle-to-grave data were considered; ²The density of concrete was considered to be 2400 kg/m³; ³The density of wood was considered to be 650 kg/m³; and 4The density of wood was considered to be 650 kg/m³.



Three different values were used to estimate the

CO2eq emissions of the Brazilian electricity matrix:

(1) minimum value (FCO2min): 0.025 kgCO2eq/kWh;

(2) median value FCO2med: 0.064 kgCO2eq/kWh; (3)

maximum value (FCO2max): 0.135 kgCO2eq/kWh,

according to data collected by the Ministry of

Science and Technology (Ministério de Ciência e

Tecnologia – MCTI (MINISTÉRIO…, 2016)). As

a result, there were six scenarios for the operational

phase for each house:

(a) FCO2 min and full- time schedule of ocupation

(FCO2min full);

(b) FCO2 min and part- time schedule of ocupation

(FCO2min part);

(c) FCO2 med and full- time schedule of ocupation

(FCO2med full);

(d) FCO2 med and part- time schedule of ocupation

(FCO2med part);

(e) FCO2 max and full- time schedule of ocupation

(FCO2max full); and

(f) FCO2 max and part- time schedule of ocupation

(FCO2max part).

The energy used for cooking comes from LPG,

assuming a consumption of 13 kg of LPG per

month. Also, a 2.98 kgCO2eq/kg ratio

(INTERGOVERNMENTAL…, 2006) was

adopted. The values of the operational stage were

calculated for the stipulated 50-year lifespan of the

house.

Maintenance stage

The CO2eq emissions from maintenance for

replacing used materials in the houses were

analyzed. To calculate the maintenance intervals,

data from the Brazilian building performance

standard (ABNT, 2013) were used, resulting in

replacement factors (RF). The same method was

used by Paulsen and Sposto (2013), Atmaca and

Atmaca (2015) and the other authors presented in

Table 3.

The interior walls presented the largest difference

when comparing the Brazilian RF and the mean

value from other studies. A service life of 20 years

was assumed for light steel framing and gypsum

interior walls, resulting in a RF of 2.5. Whereas for

the brick masonry system, a service life of 40 years

for mortar covering was assumed, leading to a RF

of 1.3. The transport of building materials and

components used in maintenance were taken into

account, adopting the same assumptions of the

construction phase. The transport distance of

replaced materials to landfills was assumed to be 20

kilometers from the building site during the

maintenance phase. The demolition/deconstruction

and disposal of these materials were allocated to the

end-of-life phase. The end-of-life method is better

detailed in the end-of-life phase section.

Table 3 - Replacement factor (RF) in different studies

Building

component

Tre

ola

r et

al.

(19

99

)1

Ch

en e

t a

l.

20

01)1

Keo

leia

n e

t a

l.

20

00)1

Sch

euer

et

al.

(20

03

)1

Ch

au

et

al.

(20

07

)1

Din

g (

20

07)1

Pa

uls

en a

nd

Sp

ost

o (

20

13

)

Atm

aca

an

d

Atm

aca

(2

01

5)

Mea

n²

Th

is s

tud

y³

Country Australia Hong

Kong USA USA

Hong

Kong Australia Brazil Turkey - Brazil

Walls

(Exterior) 1.1 1 - 1 1 1 1.3 1.1 1.1 1.3

Walls

(Interior) 1.1 1 - 1 1 2.4 2.5 1.1 1.4 1.3-2.5

Doors - 1.3 - 1.5 - 1.5-2 1.3 2 1.6 1.3

Windows - 1.3 2 1.9 - 1.5 1.3 2 1.7 1.3

Roof - 1.3 2 3.75 2.5 2.4 2.5 2 2.6 2.5

Floor 4 3 2.5 4.16 2.5 3 3.8 3 3.2 3.8

Paints 8 5 5 15 5 6-8.6 - 5 7.6 10

Ceiling 2 2 - 3.75 2.5 4 - 3 2.7 3

Note: 1Information obtained from Atmaca and Atmaca (2015). ²Average value from studies. ³Based on NBR 15575-1 (ABNT, 2013).



End-of-life phase analysis

In the end-of-life phase, it was assumed that the

building with brick masonry was demolished and

the generated waste was transported to the nearest

landfill, located 20 kilometers from the building

site. The building with light steel framing was

assumed to have been deconstructed and the

assumed generated waste transported to the nearest

landfill.

The end-of-life phase was divided into three stages:

(a) demolition/deconstruction;

(b) waste transport to the landfill; and

(c) waste disposal in the landfill.

Values of 0.00247 kgCO2/kg were used for the

demolition (ceramic brick masonry) and 0.000092

kgCO2/kg for deconstruction (light steel framing),

based on Pedroso (2015) primary data. For the

transport to the landfill, the same emission data

were used for the truck transportation of building

materials. For waste disposal activities performed in

the landfill, a ratio of 0.37 L of diesel per 1 tonne of

waste was assumed, an average value obtained from

Bovea and Powell (2016) considering that one liter

of diesel is equivalent to 2.63 kg CO2eq

(MINISTÉRIO…, 2013).

According to IAB (INSTITUTO…, 2016),

currently in Brazil about 30% of all the steel

produced comes from recycling. Usually, this

recycled steel has already been accounted for in

terms of the recycled content in steel production,

using one of the approaches presented by Bergsma

and Sevenster (2013). Therefore, the benefits of

steel recycling in light steel framing were not

considered. The only difference between steel and

other materials is the third stage (3). Steel does not

go to landfills; therefore it produces no emissions in

this phase. Its transport distance to a recycling plant

was assumed to be the same as that of other

materials to a landfill.

Design guidelines for low carbon social housing

The design guidelines for low carbon social housing

were given based on the quantitative results of

CO2eq emissions during the houses’ life cycle. Each

phase of the life cycle was analyzed individually

and, in the end, their impact in terms of total CO2eq

emissions was verified, and the guidelines were

classified according to priority (high, medium-high,

medium and low). Some suggested guidelines,

based on the literature, were generic or not

evaluated in this study. However, some points

should be addressed in future studies.

Although this paper presents a case study with some

particularities, such as the evaluation of thermal

performance just for the city of Brasilia, the authors

believe that these guidelines could be an important

contribution for continuous research in the field of

low carbon buildings.

Results and discussion

Construction phase

For the construction phase, values of 0.38 tCO2eq/m²

and 0.32 tCO2eq/m² (ECO2E) were found for the

brick masonry and for the light steel framing

houses, respectively. Comparing the ECO2E values,

the difference was 16% with a lower value for the

light steel framing system. A comparison of the

different house systems in terms of mass and

ECO2E is shown in Figure 3.

Figure 3 - Share of the house systems in mass and ECO2E for the construction phase

ECO2E - Extraction, processing of raw materials



For both houses, the walls had the greatest mass

(77% for brick masonry and 46% for light steel

framing) and ECO2E (56% for brick masonry and

46% for light steel framing). These results show the

importance of choosing an adequate wall system in

a low carbon footprint social housing design. The

share of materials and components of each

building’s wall system in terms of mass and ECO2E

is presented in Figure 4.

The extraction and processing of raw materials were

responsible for 97% of the total ECO2E for brick

masonry and 94% for light steel framing. The

transportation, on the other hand, played a small

role, with 3% for brick masonry and 6% for light

steel framing.

For the transport phase, the mass of the light steel

framing was 57% less than the mass of the brick

masonry. However, the results of ECO2T show

0.011 tCO2eq/m² for brick masonry and 0.019

tCO2eq/m² for light steel framing. The farther

distances traveled by materials and components of

light steel framing exceeded the impact of higher

mass values of the brick masonry system.

Therefore, to minimize the CO2eq of the transport

phase, it is important to specify during the design

phase low mass materials and components located

near the construction site.

Use phase

The use phase was composed of operational and

maintenance phases. The operational CO2eq

emissions due to air conditioning ranged from 0.08

tCO2eq/m (FCO2min partial) to 0.68 tCO2eq/m²

(FCO2max full) for the brick masonry house and 0.10

tCO2eq/m² (FCO2min partial) to 0.83 tCO2eq/m²

(FCO2max full) for the light steel framing house. The

total operational CO2eq emissions (considering air

conditioning, equipment and cooking) are presented

in Figure 5.

The brick masonry presented a better thermal

performance for the city of Brasília, due to the

greater thermal capacity of the walls. According to

NBR 15220-3 (ABNT, 2005) for Bioclimatic Zone

4, it is more advantageous to use heavy walls in

buildings. Hence, this masonry system was

expected to present the best thermal performance.

However, considering the growing interest in light

steel framing systems in the Federal District region,

this study evaluated the impact of the thermal

performance of light steel framing on life cycle

carbon emissions.

The CO2eq emissions due to the electricity

consumption for the six scenarios, including the air

conditioning use, played a small role (14-23%) in

ECO2O for the FCO2min and a greater role (48-62%)

for the FCO2max (Figure 6).

The variation of CO2eq emissions in this phase is due

exclusively to the consumption of air conditioners

because of the differences in thermal performance

of the different facades of brick masonry and light

steel frame buildings, considering the two schedules

(part-time and full-time occupations) and the three

CO2eq factors from electricity (FCO2min, FCO2med

and FCO2max). The cooking process was considered

the same for both buildings.

The cooking process generates more CO2eq per

energy. Considering FCO2max, its emissions (LPG)

are almost twice the emissions from the electricity

used for equipment. In relation to the FCO2min, the

difference is almost four fold. Therefore, one

important strategy to reduce operational emissions

when pursuing a low carbon social housing design,

especially for a FCO2min scenario, is to reduce the

LPG use or substitute it for a less CO2eq fuel, for

example, natural gas, since it emits less CO2eq than

the LPG.

Figure 4 - Share of wall building components in mass and ECO2E in the construction phase

ECO2E - Extraction, processing of raw materials



Figure 5 - Comparison of operational CO2eq emissions for the six scenarios

Figure 6 – Cooking, equipment and air conditioning share in the ECO2O phase

Regarding equipment, it is important to use pieces

that consume less electricity. In Brazil, it is

recommended to use label-A equipment as ranked

by Procel. The electric shower accounted for the

highest energy consumption and CO2eq,

representing 35.5% of emissions of electrical

equipment, requiring designer’s attention for low

carbon social housing projects. One alternative is to

install solar panels for water heating, a suggestion

that is encouraged in the “My House, My Life”

Program. Nevertheless, it is necessary to consider

the embodied CO2eq due to material installation,

replacement and end-of-life during the building’s

life cycle.

Concerning the maintenance phase, the results of

ECO2M for brick masonry and light steel were 0.19

tCO2/m² and 0.24 tCO2/m², respectively. The larger

values for the light steel framing house are due to

the gypsum board substitution (20 years), and OSB

board and rock wool substitution (30 years);

meanwhile, the mortar and plaster were considered

to have a service life of 40 years. The mass and

ECO2M for the houses are compared in Figure 7.

The paint system was responsible for great CO2eq

emissions because of the low service life considered

(5 years) and the high value of embodied CO2eq of

paints, 1.99 kgCO2eq/kg. Therefore, to minimize the

impacts of the maintenance phase it is important to

specify, during the design phase, materials with low

values of CO2eq emissions and high durability.

End-of-life phase

For the end-of-life phase, 0.0063 and 0.0024 tCO2eq

per m² were recorded for the brick masonry and the

light steel framing houses, respectively (Figure 8).

The end-of-life phase considered in this study

consisted of demolition (for brick masonry) and

deconstruction (for light steel framing), as well as

waste transportation and disposal activities in the

landfill. Assuming that transport distances were the

same for the brick masonry and the light steel

framing houses, the difference in the results

reflected the mass of the wall systems and the

processes used in demolition and deconstruction.

The deconstruction process of the light steel

framing resulted in less CO2eq than de demolition

process of brick masonry. The waste transport was



influenced by the mass and distances to the landfill.

In addition, the waste disposal was influenced by

the mass of waste. Therefore, in order to decrease

carbon emissions of the end-of-life phase, it is

important to prioritize a deconstruction process

over demolition, have material wastes with lower

masses and choose shorter distances to disposal,

reuse or recycling plants from the building location.

Overall life cycle balance

The results of ECO2TOT for brick masonry and

light steel framing houses for the six scenarios are

presented in Figure 9.

Figure 7 - Share of the house systems in mass and ECO2M for maintenance stage

ECO2M- Maintenance phase

Figure 8 - Comparison of end-of-life CO2eq (ECO2EL) emissions

Figure 9 - Total life cycle CO2eq emissions assessment



The light steel framing house presented larger

values of total CO2eq emissions (ECO2TOT) than

the brick masonry house in all scenarios. The brick

masonry house presented values ranging from 1.16

tCO2eq/m² to 1.76 tCO2eq/m² and the light steel

framing presented values ranging from 1.17

tCO2eq/m² to 1.91 tCO2eq/m².

The biggest difference between light steel framing

and brick masonry houses (8%) was seen in the full

time schedule using the FCO2max. In this sense, the

choice of FCO2 for electricity in this study and in the

Brazilian context was an important and critical

factor. This is because depending on the FCO2 used

there is an increase or decrease in the thermal

performance impact on the life cycle carbon

emissions.

In Figures 10 and 11, the life cycle carbon emissions

for brick masonry and light steel framing houses are

presented over time. The black arrows indicate the

points on the graph that represent the maintenance

phase due to the replacement of materials and

components.

The share of each phase in the whole life cycle of

the houses for the six scenarios is shown in Figure

12.

Figure 10 - Life cycle CO2eq emissions over time for ceramic brick masonry house

Figure 11 - Life cycle CO2eq emissions over time for light steel framing house



Figure 12 - Share of each phase in the life cycle carbon emissions assessment

ECO2C– Construction phase. ECO2O- Operational phase. ECO2M- Maintenance phase. ECO2EL- End-of-life phase

The CO2eq emissions of the operational phase

accounted for the highest share of the total

building’s life cycle, varying from 50 to 70%. In the

construction phase, it varied from 20 to 30%, in the

maintenance phase, from 11 to 20%, and in the end-

of-life, it was lower than 1%. It is very important to

know which phase has a bigger impact on the

carbon life cycle of a building, indicating what the

designers should give more attention to during the

design stage.

Design guidelines for low carbon social housing

Finally, based on the results obtained in this study,

design guidelines for low carbon social housing

were developed (Table 4), as a way to guide

designers and builders.

There are different ways for designers to reduce the

carbon footprint of a social housing project, as

presented in Table 4. However, it is important to

define the critical and priority items that result in

greater and more effective CO2eq reduction. In this

sense, the high ones (in red) deserve a greater

attention from designers.

Although not evaluated in this study, bioclimatic

architecture principles are very important to

consider in the design phase. Features such as

crossed ventilation, adequate shading and

vegetation, correct openings for heated air outlet,

natural lighting, adequate solar orientation and

others can help minimize buildings’ energy

consumption. The use of these strategies related to

CO2eq of buildings could be evaluated in future

research studies.

Conclusions

This study used the LCCO2A to investigate CO2eq

emissions during the life cycle of two typical social

house projects in Brasilia, Brazil. The variables of

the study were the external and internal wall

systems of the houses, with other parts remaining

unchanged. A brick masonry house was compared

with a light steel framing system, an industrialized

system starting to gain popularity in the country.

The assessment was conducted from a cradle-to-

grave perspective, including the construction, use

(operation and maintenance) and end-of-life phases.

The CO2eq emissions from the construction phase

were 0.38 tCO2eq/m² for the brick masonry house

and 0.32 tCO2eq/m² for the light steel framing house.

For the operational phase, the emissions varied

from 0.59 to 1.19 tCO2eq/m² for the brick masonry

house, and 0.61 to 1.33 tCO2eq/m² for the light steel

framing house, corresponding to 50-70% of the

total life cycle emissions. The emissions due to

maintenance were 0.19 tCO2eq/m² for the brick

masonry, and 0.24 tCO2eq/m² for the light steel

framing. The emissions from the end-of-life phase

were lower than 1% for both houses.

Comparing the different systems of the houses

(walls, roof, floor, painting and installations), the

wall systems presented the biggest share in terms of

mass and CO2eq emissions for both houses. The

paint system played the biggest role in terms of

CO2eq emissions in the maintenance phase.

The brick masonry house presented less total CO2eq

emissions than the light steel framing house. The

difference between the total emission values varied

from 2% to 8%. This indicates that the light steel

framing system for the city of Brasilia would not be

a recommendable alternative in terms of CO2eq

emissions for the kind of buildings evaluated in this

study.



Table 4 - Design guidelines for low carbon social housing

Phases Stages Design guidelines Priority

Construction

Extraction, processing

of raw materials

Specification of materials, components and systems

with low values of embodied CO2eq emissions and

adequate thermal performance according to the location

of the building. The wall system was responsible for a

great share of mass and CO2eq emissions in this phase,

thus deserving special attention.

High

Transport


with lower mass (it is important not to forget the

thermal performance) and located near the construction

site.

Low

Use

Operational

Electrical equipment (no air conditioning): use of

efficient equipment that consumes less electricity. Use

of label-A equipment as ranked by Procel is

recommended. The electric shower was the equipment

that consumed the greatest share of electricity in social

housing. Therefore, the installation of solar panels to

heat water could be an option. The embodied carbon of

materials and components and end-of-life of solar

panels must be accounted for in the analysis. In a high

FCO2eq scenario for the Brazilian electrical matrix, this

phase becomes more important.

Medium-

High

Cooking: using natural gas instead of LPG for cooking

could be a good alternative to reduce CO2eq emissions of

buildings.

High

Air conditioning: the specification of building systems

with appropriate thermal performance to the building

location is important because it will result in lower

energy consumption by artificially cooling of the

building. This will vary depending on the construction

system adopted, location and climate zones. In a high

FCO2eq scenario for the Brazilian electrical matrix, this

phase becomes more important.

Medium-

High

Maintenance


with higher service life. Bear in mind the correct

maintenance of the systems in order to extend service

life and avoid total replacement of the given material,

component or system.

Medium

End-of-life

Deconstruction/Demo

lition

Specification of systems that can be deconstructed or

removed instead of being demolished. Low

Waste transportation

Specification of building systems with lower mass and

choice of disposal sites (landfill, recycling plant,

incineration facility, etc.) near the building location.

Low

Waste disposal Specification of building systems with lower mass to

decrease diesel consumption in disposal activities. Low

The results also showed the importance of

considering different CO2eq emission factors in the

Brazilian context in the operational phase. Finally,

based on the results obtained, design guidelines for

low carbon social housing were proposed.

It is important to emphasize that some data were

taken from foreign literature (mainly for the light

steel framing). There is a lack of consolidated

Brazilian database of CO2 emissions for building

materials. There are only some separate initiatives

in some sectors, such as cement and ceramic. When

this complete environmental database for Brazilian

building materials is published, the authors intend

to verify the calculations and the differences in

results.

For future research studies, it is recommended to

evaluate other environmental aspects, such as water

consumption, waste generation and recycling

potential of building materials. Other Brazilian

systems (both conventional and industrialized ones)



should be evaluated, such as concrete brick

masonry and concrete walls, as well as other

Brazilian regions.

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Lucas Rosse Caldas Program of Civil Engineering | Federal University of Rio de Janeiro | Cidade Universitária, Centro de Tecnologia, Bloco B, Ilha do Fundão | Rio de Janeiro – RJ – Brazil | CEP 21945-970 | Tel.: +55 (62) 99672-7202 | E-mail: [email protected]

Júlia Santiago de Matos Monteiro Lira Dept. of Civil and Environmental Engineering | University of Brasília | Faculdade de Tecnologia, SG-12 Mestrado em Estruturas e Construção Civil, Campus Universitário UnB Darcy Ribeiro, Asa Norte | Brasília –DF – Brazil | CEP 70910-900 | Tel.: +55 (61) 98290-8666 | E-mail: [email protected]

Pedro Corrêa de Melo Dept. of Civil and Environmental Engineering | University of Brasília | Tel.: +55 (61) 99905-8321 | E-mail: [email protected]

Rosa Maria Sposto Dept. of Civil and Environmental Engineering | University of Brasília | Tel.: +55 (61) 3274-1517 | E-mail: [email protected]

Revista Ambiente Construído Associação Nacional de Tecnologia do Ambiente Construído

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